avoid_single_child_in_multi_child_widgets

v0.1.0 Warning Widget Best Practices

Flags a multi-child widget whose children list holds exactly one element.

A Column with one child does the same thing as the child on its own, plus a layout pass and a level of nesting. Whatever you actually wanted — alignment, padding, sizing — has a single-child widget that says so in its name.

Reported for Column, Row, Wrap, Flex, SliverList, SliverMainAxisGroup, SliverCrossAxisGroup, SliverChildListDelegate, and MultiSliver from sliver_tools.

This rule is in the opinionated preset, so it is on with preset: opinionated and preset: pedantic. No configuration.

See also: Column | Row

Don’t

Scaffold(
  body: Column(
    children: [Text('I am the only child')],
  ),
)

Do

Scaffold(
  body: Text('I am the only child'),
)

Reach for the single-child widget that names the intent

Most one-child Columns exist for an alignment or spacing property. Each has a direct replacement:

// Don't
final bad = Column(
  mainAxisAlignment: MainAxisAlignment.center,
  children: [Text('Loading')],
);

// Do
final good = Center(child: Text('Loading'));

// Don't
final bad = Row(
  children: [
    Padding(padding: EdgeInsets.all(16), child: Text('Total')),
  ],
);

// Do
final good = Padding(padding: EdgeInsets.all(16), child: Text('Total'));

Slivers too

// Don't
final bad = CustomScrollView(
  slivers: [
    SliverMainAxisGroup(
      slivers: [SliverToBoxAdapter(child: Text('Header'))],
    ),
  ],
);

// Do
final good = CustomScrollView(
  slivers: [SliverToBoxAdapter(child: Text('Header'))],
);

Known limitations

A list whose single element is a spread (...items), a collection-for, or a map entry is not reported — the number of children at run time is not one:

// Not reported: `...items` may expand to any number of children
Column(children: [...items])

An if element counts as one child only when every branch it has is itself a plain widget, so Column(children: [if (isWide) Text('a') else Text('b')]) is reported while Column(children: [if (isWide) ...wideParts]) is not.

Only a list literal is examined. Column(children: buildRows()) is opaque and left alone.

Turning this rule off

many_lints.yaml

rules:
  avoid_single_child_in_multi_child_widgets: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• avoid_flexible_outside_flex — Only use Flexible and Expanded as direct children of Row, Column, or Flex.
• prefer_for_loop_in_children — Prefer collection-for syntax over functional list building in widget children.
• avoid_returning_widgets — Extract widget helper methods into separate widget classes.
• avoid_too_many_widgets_per_build — Keep one build method within a widget budget.